Modern cars and trucks include rearview mirrors mounted inside and outside of the vehicle. One type of conventional interior rearview mirror comprises a prismatic mirror that can be switched from a first orientation suitable for normal driving conditions to a second orientation, which reduces glare caused by headlights of vehicles approaching from the rear.
Recently, electrochromic rearview mirrors have been developed which automatically change from a fill reflectance mode during the day to a partial reflectance mode during the night for glare protection. Electrochromic rearview mirrors typically comprise a relatively thin electro-optic medium sandwiched and sealed between two glass elements. In most assemblies, when the electro-optic medium is electrically energized, it darkens and absorbs an increasing amount of light as the applied voltage is increased. When the electrical voltage is removed, the mirror returns to its clear state. Examples of such automatic rearview mirrors are disclosed in U.S. Pat. Nos. 4,902,108; 4,917,477; 5,128,799; 5,202,787; 5,204,778; 5,278,693; 5,280,380; 5,282,077; 5,285,060; 5,294,376; 5,682,267; 5,689,370; 5,448,397; 5,451,822; and 5,818,625 each of which is assigned to the assignee of the present invention and each of which is incorporated herein by reference.
In the past, information such as the words "HEATED" or "OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR" have been used on many vehicle rearview mirrors. In addition, some types of automatic rearview mirrors have included compass and temperature readings. However, such conventional rearview mirror displays typically comprise a glossy planar surface, which makes the display difficult to read. Furthermore, such conventional displays are often difficult or impossible to read by some occupants of a vehicle. For example, interior rearview mirrors are typically angled toward the driver and away from the front seat passenger, thereby obstructing the front seat passenger's ability to see the display. In addition, selectable information displays commonly used in automobile interiors comprise complex electronic assemblies. This type of display is not only expensive, but also more prone to failure due to the number and complexity of components.
In addition to the problems and concerns discussed above with displays on mirrors, there are additional problems that need to be addressed. One way of forming the individual letters of the words "HEATED" and "OBJECTS IN OR . . . " is to apply reflector material to an electrochromic mirror subassembly as a uniform layer, and then selectively remove portions of reflector material to form the shape or image of detailed alphanumeric and symbolic indicia in the reflector material. However, it is difficult to remove the reflector material in a manner that accurately and consistently forms all parts of small letters and symbols, such that the removal process potentially results in significant scrap. This scrap can be very expensive because, not only does a significant percentage of scrap result from imperfect indicia images, but further the mirror subassembly is relatively expensive work-in-process at that point in the manufacturing process. Concurrently, the scrap is difficult to repair.
Another problem is that, even if reflector material is accurately removed to form the indicia image, many manufacturers want color in their displays to improve their customer appeal. Colored translucent labels have been used in the past in vehicles, such as in instrument panels, to create visual displays. However, there are problems with known prior art labels used in the environment of a mirror. For example, stick-on labels using adhesive may partially delaminate from glass mirror element over time, leading to poor appearance where the released adhesive has a discontinuous and patchy appearance. Also, the adhesive can trap air during the installation process, leading to immediate poor appearances or leading to in-service delamination problems as the stick-n label and its carrier are thermally cycled.
Alignment of components and displays in mirrors is another important consideration in regard to customer acceptance. Display information that is non-parallel and angled relative to a perimeter of the mirror can result in a customer forming a very poor opinion of the quality of a vehicle, even though the mirror is fully functional. Further, misalignment can be very aggravating to a customer, because the customer sees the misalignment problem every time they look in the mirror, which occurs every time they are in the vehicle.
Another problem is accurate positioning and retention of a printed circuit board in the mirror housing. Printed circuit boards carry circuits used in electrochromic mirrors to control darkening for glare protection, and also carry other circuits and sensors, such as for daylight sensing, keyless entry signal sensing, information displays, and the like. It is important that the printed circuit board be accurately positioned so that any light sources and sensors carried thereon are accurately located, and so that any control buttons for the mirror that are mounted on the printed circuit board and protrude through a face of the housing are also properly and accurately positioned. Additionally, it is noted that the printed circuit board should be firmly held in a manner preventing ratting, but in a manner not leading to breakage, fracturing, or undue bending or stressing of the printed circuit board during assembly and during thermal cycling while in service.
Another less obvious problem concerns secondary reflections and scattering of light within transparent layers in the mirror subassembly. Electrochromic mirror subassemblies include a pair of transparent elements, such as flat glass elements, with a chamber therebetween. The chamber is filled with electrochromic material that includes a first layer of transparent conductor material and either another layer of transparent conductor (if the mirror subassembly is a fourth surface reflector), or a reflector/electrode (if the mirror subassembly is a third surface reflector). When light is introduced through an opening in the reflector, a primary amount of the light travels through the transparent elements and through the associated layers of electrochromic material without unacceptable distortion. However, a small amount of the light is reflected as the light passes through each of the interfacing surfaces in the mirror subassembly. This can lead to double images (sometimes called "ghosting"), blurred images, shadowing, and/or the occurrence of undesirable scattering of light across a visible face of the mirror subassembly. This is undesirable because it reduces the clarity of the visual display and can, in extreme cases, be interpreted by a customer as a defect.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.